A screen grab from a "box only" ad on Craigslist. It's not the only such ad that you'll find.

Craigslist screen grab

A quick scan of Craigslist reveals a curious market for not just smartphones and computers but the empty packaging of smartphones and computers. On my local Craigslist, a MacBook Pro box — "box only," as the sales pitches read — goes for $19. A MacBook Air box will cost you $15. And a Samsung Galaxy S4 box sells for $10.

This box market seems limited to the smartphone, tablet and computer packaging, and not boxes for, say, televisions or jewelry. Sure, a lot of computer packaging can be impressive in its engineering to fit all components snugly. But $19 for a box? What's going on here? We're hoping you can tell us.